1. Field of the Invention
The present invention relates to fluorophosphate glasses which are colorized blue for the use as filter glasses.
2. Description of Related Art
Basically, fluorophosphate glasses for use as filter glasses are known in prior art. But these glasses have the disadvantage that their weathering resistance is poor and that their production is difficult due to their often very high content of fluorine, since fluorine itself and the fluorides of many glass components are volatile under the conditions of common production methods. Therefore, a lot of efforts have been made to optimize the compositions of fluorophosphate glasses with the target of obtaining glasses which on the one hand have good stability and on the other hand can be obtained through economic production methods. Furthermore, the glasses according to the present invention have a very steep absorption edge. This means that the above-mentioned range of high transparency in a range of 338 to 640 nm steeply passes into a range of low transparency. With other words, the transmission curve has in wave length ranges which are adjacent to the range of high transparency a high (positive or negative) slope. So it is achieved that color aberrations are reduced.
Thus it is the object of the present invention to provide fluorophosphate glasses which solve the problems of prior art.